Non-tear seams produced by radio frequency means

ABSTRACT

Layers of fabric containing thermoplastic fibers are bonded together by radio frequency means along a seam, the seam being comprised of fused thermoplastic fibers with the intensity of fusion varying from a maximum along a maximum bond area to a minimum along the edge of the seam to prevent the formation of a tear line between the fabric and the seam.

NON-FEAR SEAMS PRODUCED BY RADIO FREQUENCY MEANS 2 Sheet s-Sheet 1 FIG.3.

RADIO FREQUENCY -l4 SOURCE L. GIDGE FIG.

Original Filed Sept. 11, 1970 May 7, 1974 FIG. 2.

L. GIDGE 3,809,596

NON-FEAR SEAMS PRODUCED BY RADIO FREQUENCY MEANS May 7, 1914 2Sheets-Sheet 2 Original Filed Sept. 11, 1970 FIG. 4.

Rww\\ FIG 6.

FIG. 5.

FIG. 7.

United 1am FREQUENCY MEANS Lester Gidge, Nashua, N. H., assignor to,onsanto Company, St. Louis, Mo. I Original application Sept. 11, 1970,Ser; No. 71,554, now Patent No. 3,725,189. Divided and this applicationMar. 14, 1972, Ser. No. 234,490 W I x Int. Cl. B29c 27/02 l Y 09,s9a...NON-TEAR SEAMSPRODUCED. BY RADIO U.S. Cl. 156-380 1 ABSTRACT on THEnrscLosunn' Layers of fabric containing thermoplastic fibers are bondedtogether by radio frequency. means alonga scam, the seam. beingcomprised of fused .thermoplastic. fibers with the intensity of fusionvarying from a maximum along a maximum bond area to a minimum along theedge of the seam to prevent the formation of a tear line between thefabric andthe seam.

This is a division, or application seto. 71,554 "filed Sept. 11, 1970,now PaLNo". 3,725,189. BACKGROUND OF THE INVENTION 1 Field of theinvention This invention relates to seam'bonded fabric by radio.frequency means and, more particularly, to'aseamwhich joins at least twofabrics containing thermoplastic fibers together without a tear linebeing formed between the fabric and the seam. (2) Description of'theprior art.

The basic invention of bon'ding'thrmciplzistidfabric together by radiofrequency means without arcing through the fabric is disclosed in mycopendingiapplication, .Ser. No. 71,656, filed Sept. 14, 1970, now Pat.No. 3,671,708. Arcing, which is an electrical discharge betweentheelece. trodes and which occurs along the sidesf of the electrodes, isprevented by recessing the electrodes ina dielectric resilient member.The dielectrioresilie'rit.rnernber e ng. tacts the fabric and fills thevoidstherein along. an' area".

adjacent'the edge of the electrodeLBy eliinii'iating-the voids, arcingis prevented. I

U.S. Pat. 2,517,672 to Jenkins shows a slightly crowri'ed electrodeflanked by 'a'rigid dielectric material which is used to support plasticsheets between' the electrodes. However, Jenkins relates only to the:bondingof plastic sheet material and not to the bonding 'of fabricwhether the fabric be woven or hon-wovemfonthe reason that the radiofrequency bonding of fabric .would be -impossibleby the Jenkins or anyother prior art process. .1

SUMMARY QFTHEINYENTIQNA.

While this invention is'adaptablefor use on planar at ticles containingmeltable thermoplastic materials, it is most adaptable on knit ted,woven-and non-woven fabric comprised essentially of thermoplasticfibers, thelmole+ cules of which becoming excited when exposed to radiofrequency power, said fibers being such as nylon, vinyl chloride,vinylidene chloride and cellulose acetate. This invention is especiallyadaptable for use on synthetic spunbonded fabric as described in U.S.Pats. 3,516,900, 3,276,944 and 3,341,394. The apparatus is comprised ofa pair of movable electrodes, means for supplying radio frequency powerto the electrodes and a resilient insulating member, such as a siliconerubber, which flanks the sides of a selected electrode. The selectedelectrode is recessed a distance in the resilient insulating member andis provided with a convex terminus. The resilient insulat- 3,809,596Patented May 7, 1974 fabric-layers by filling the voids in the fabric.With the fabric layers between the electrodes, the electrodes areadaptable for moving towards each other to compress the fabric layersinto intimate contact such that bonding occurs between the fabric layersupon the activation of the electrodes with radio frequency power.

' The article of manufacture itself is comprised of at least two :layersof fabric which contain thermoplastic fibers and a seam which joins thefabrics together. The seam is comprised of fused thermoplastic fiberswith the intensity of fusion varying from a maximum along a maximum bondarea located approximately in the center of the seam to a minimum alongthe edges of the seam. Thus, the seam shape taken in cross-section is ofa general sloping depression, the shape of which does not produce asharply creased indentation which might serve as a tear line at thejuncture between the seam and the fabric. With the intensity ofinterfilament fusion increasing from the edge of the seam to the center,energy must be extended to rupture all of the filaments from the pointof substantially no interfilament fusion to the point wheresubstantially all of the filaments have been fused in order to causefailure of the fabric along the scam.

, Therefore, an object of this invention is to provide a seam forjoining fabric containing thermoplastic fibers together which does notpresent a tear line.

- Another object of this invention is to provide an apparatus for.forming a seam between two fabrics containing thermoplastic fibers suchthat the energy for rupturing the seam is substantially equivalent tothe energy for rupturing either one of the fabrics comprising the seam.

DESCRIPTION OF THE DRAWINGS "FIG. 1 is an enlarged section view of theelectrode arranged in accordance with the principles of the inventionand. showing the same with two layers of fabric placed therebetween;

FIG. 2 is an enlarged view of FIG. 1 showing the electrodes in contactwith the fabric and in a position to bond the fabric in the area betweentheelectrodes;

FIG. 3 is a view in cross-sectionof a fabric having a bonded seam'formed'by a conventional method using adio frequency means and showing theformation of tear lines between the seam and the fabric;

FIG. 4 is an enlarged section view of the fabric having: been joined bythe seam of this invention;

FIG. 5 is an alternative embodiment of the electrode of FIG. 1 andshowing an apparatus adaptable for forming a seam having a tear linealong one edge but preventingthe formation of a tear line along theother edge;

'j FIG. 6 is the section of FIGS wherein the electrodes are incontactwith the fabric; and FIG. 7 is the seamed fabric produced by theapparatus as shown'in FIG. 5. i f

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT While the apparatus 'ofthis invention is operative on practically any fabric regardless ofconstruction as long as it contains at least a significant portion ofthermoplastic fibers, this invention is best illustrated by usingspun-bonded non-woven fabric as disclosed in U.S. Pat. 3,516,900. Thefilaments of these fabrics are wholly thermoplastic and are bondedtogether at a substantial number of filament cross-over points withoutthe use of extraneous binder material. The fabric described in U.S. Pat.3,516,900 is comprised of continuous nylon filaments bonded together ata substantial number of filament cross-over points by the absorption andsubsequent removal of a hydrogen halide gas. Thus, the non-woven fabricis comprised completely of nylon.

Fabrics and 11 which are to be bonded together by means of a seam arepositioned between upper electrode 12 and lower electrode 13. The radiofrequency energy a required for bonding the fabrics together is suppliedby radio frequency source 14. Radio frequency source 14 is connected toelectrodes 12 and 13 by lines 15 and 16, respectively. Upper electrode12 is mounted in movable housing 17 and is provided with terminus 18which'is arcuated in shape and which is recessed in resilient insu.

lating member 20. Resilient insulating member 20. is re-: tained byhousing arms 21 which insure that resilient mem-. ber penetrates thefabric interstices. v,

The apparatus as shown in FIG. 1 is in a normal at rest position withterminus 18 of electrode 12 being recessed in resilient member 20 andout of contact with fabric 10. FIG. 2 represents the position of theelectrode when bonding is to occur to form the seam. With suf-- ficientpressure which may range from 5 to or more pounds per linear inch ofelectrode width depending upon the softness of the fabric, resilientinsulating member 20 fills the voids in the fabric adjacent the upperelectrode 12 and prevents arcing through the fabric. Arcing betweenelectrode 12 and electrode 13 occurs, if at all, along the exteriorsurfaces of electrode 12 and not directly beneath the same. Therefore,with resilient insulating member 20 penetrating the fabric, the airwhich is necessary for electrical discharge, is removed and arcing isprevented.

FIG. 3 represents a seam bonded layered fabric structure having tearlines and is comprised of fabrics 22 and 23 and seam 24. It can be seenthat seam 24 throughout its length A (maximum bond area) is sharplyindented from the surfaces of fabrics 22 and 23, the unbonded fabriclength being represented by C. The structure is either comprised ofcompletely fused and immobile fibers along A or fibers completely freeof fusion along C. Thejunction between A and C form tear lines for thefibers of C are cantilevered from A and the force for rupturing thefibers at the A and C junction is the force necessary only to shearthose filaments because fiber movement at the mentioned junction isprevented. Thus, it can be seen that if the formation of a tear line isto be prevented, a transition state between A and C is necessary, thetransition state being where the fibers are neither completely fused norcompletely free of fusion. p

FIG. 4, which is the article of'this invention, is comprised of fabricsand 31 which are joined together by seam- 32. The fabric underC-represents fabric the fibers of which are completely free of fusion.The fabric under A is' the maximum bond'area and represents fabric thefibers of which have been'completely fused, 'The fabric under B which isthe diminishing bond area is the transition state where the filamentsare neither completely fused nor completely free of fusion. Thus, theline between B and C represents the beginning of fiber fusion with agradual increase in'the intensity of fusion until the line 'between Band A is reached whereupon substantially all of the filaments have beencompletely fused so as to lose their identity. Since interfilamentfusion is incomplete along B, the fibers upon being subjected to atearing force are able to move and to redistribute the applied load soasto prevent the formation of a shear plane or tear line as was shown inFIG. 3 between A and C. Therefore i FIG. 4, the force required to tearfabric 30 from fabric 31 approaches the force required to tear eitherfabric alone, such force being substantially greater than the rce'required to tearth completely fused filaments under area A which issubstantially film-like.

- FIGS: Sfland 6 -represent an alternative embodiment of this inventionwhere the article is comprised of two fabrics and a seam. A tear line isformed along one edge of the seam but is prevented from forming alongthe other edge' The. only difference between the apparatus shown inFIGS. 5 and 6 and the apparatus shown in FIGS. 1 and 2 is tliaf'the endof upper 'electro'de'12 is provided with an arquated end 35 which has amaximum depth along oneedgeso as, to pfovidemaximum bonding along oneedge of the resulting "seam. Thus, FIG. 7'is a combination of FIGS. 3and 4 in that alongthe left hand portion, C transforms directly into Awhereas along the right hand portion, A gives way to B, the area ofincomplete fiber fusion, which in turn gives way to C, Thus, the maximumintensity of inteffiber'fusion in B is adjacent to A with the intensitydecreasing until B joins C whereupon no interfilament fusion exists atall.

From this disclosure, other embodiments of the present invention wouldbe obvious. Likewise, the lower electrode may also be provided with aresilient member with both electrodes. taking the form of rotatabledisks which would provide for an endless seam along a fabric. Also, theelectrodes may be mounted on a rotating drum which is associated with anelectrical conductive surface, such as a movable belt, which" is adaptedto bear against the pattern of the roller for a specific length of therollers arc with fusion in the formation of welds taking placesubstantially as heretofore described.

I claim:

1. A radiofrequency apparatus, for forming a fusebonded seam betweenlayers of fabriccontaining thermoplastic fibers in a manner to preventthe formation of tear lines between the seam and the fabric, saidapparatus having a pair of relatively moving electrodes capable ofcompressing the fabric layers into intimate contact with one of saidelectrodes being flanked by and being recessed in resilient insulatingmembers, means for supplying radio frequency'pow'er tosaid electrodesand means for moving said electrodes towards each other to compress'said fabrie'therebetween, the'improvement comprising said electrodebeing provided with a convex terminus and being flanked by saidresilient members for engaging said fabric,""said convex terminus' beingsubstantially flush with said: resilient members upon compression of thesame and adapted to 'contactsaid fabric so that upon the energization ofsaid electrode, the energy for fusion of the organic synthetic fibersdecreases away from the center of said convex terminus, p g V "Re ferences Cited ,UN TEDSIATEs PATENTS 2,936,816

5/1960 Lang 156--273 X 2,517,672 8/1950 "Jenkins -156--380X 3,256,527671966 Studen 156'272X 2,565,161 "8/1951 Wilmette et al. '156--274X2,638,963 5/1953 Frederick et a1. 156-273 X

